Acute B-Cell Inhibition by Soluble Antigen Arrays Is Valency-Dependent and Predicts Immunomodulation in Splenocytes

Soluble antigen arrays provide increased efficacy and safety over free peptides for tolerogenic immunotherapy

Autoantigen-specific immunotherapy using peptides offers a more targeted approach to treat autoimmune diseases, but clinical implementation has been challenging. We previously showed that multivalent delivery of peptides as soluble antigen arrays (SAgAs) efficiently protects against spontaneous autoimmune diabetes in the non-obese diabetic (NOD) mouse model. Here, we compared the efficacy, safety, and mechanisms of action of SAgAs versus free peptides. SAgAs, but not their corresponding free peptides at equivalent doses, efficiently prevented the development of diabetes. SAgAs increased the frequency of regulatory T cells among peptide-specific T cells or induce their anergy/exhaustion or deletion, depending on the type of SAgA used (hydrolysable (hSAgA) and non-hydrolysable 'click' SAgA (cSAgA)) and duration of treatment, whereas their corresponding free peptides induced a more effector phenotype following delayed clonal expansion. Over time, the peptides induced an IgE-independent anaphylactic reaction, the incidence of which was significantly delayed when peptides were in SAgA form rather than in free form. Moreover, the N-terminal modification of peptides with aminooxy or alkyne linkers, which was needed for grafting onto hyaluronic acid to make hSAgA or cSAgA variants, respectively, influenced their stimulatory potency and safety, with alkyne-functionalized peptides being more potent and less anaphylactogenic than aminooxy-functionalized peptides. Immunologic anaphylaxis occurred in NOD mice in a dose-dependent manner but not in C57BL/6 or BALB/c mice; however, its incidence did not correlate with the level of anti-peptide antibodies. We provide evidence that SAgAs significantly improve the efficacy of peptides to induce tolerance and prevent autoimmune diabetes while at the same time reducing their anaphylactogenic potential.

Multivalent Scaffolds to Promote B cell Tolerance

Autoimmune diseases are characterized by aberrant immune responses toward self-antigens. Current treatments lack specificity, promoting adverse effects by broadly suppressing the immune system. Therapies that specifically target the immune cells responsible for disease are a compelling strategy to mitigate adverse effects. Multivalent formats that display numerous binding epitopes off a single scaffold may enable selective immunomodulation by eliciting signals through pathways unique to the targeted immune cells. However, the architecture of multivalent immunotherapies can vary widely, and there is limited clinical data with which to evaluate their efficacy. Here, we set forth to review the architectural properties and functional mechanisms afforded by multivalent ligands and evaluate four multivalent scaffolds that address autoimmunity by altering B cell signaling pathways. First, we address both synthetic and natural polymer backbones functionalized with a variety of small molecule, peptide, and protein ligands for probing the effects of valency and costimulation. Then, we review nanoparticles composed entirely from immune signals which have been shown to be efficacious. Lastly, we outline multivalent liposomal nanoparticles capable of displaying high numbers of protein antigens. Taken together, these examples highlight the versatility and desirability of multivalent ligands for immunomodulation and illuminate strengths and weaknesses of multivalent scaffolds for treating autoimmunity.

Soluble antigen arrays improve the efficacy and safety of peptide-based tolerogenic immunotherapy

Autoantigen-specific immunotherapy using peptides offers a more targeted approach to treat autoimmune diseases, but the limited in vivo stability and uptake of peptides impedes clinical implementation. We previously showed that multivalent delivery of peptides as soluble antigen arrays (SAgAs) efficiently protects against spontaneous autoimmune diabetes in the non-obese diabetic (NOD) mouse model. Here, we compared the efficacy, safety, and mechanisms of action of SAgAs versus free peptides. SAgAs, but not their corresponding free peptides at equivalent doses, efficiently prevented the development of diabetes. SAgAs increased the frequency of regulatory T cells among peptide-specific T cells or induce their anergy/exhaustion or deletion, depending on the type of SAgA (hydrolysable (hSAgA) and non-hydrolysable 'click' SAgA (cSAgA)) and duration of treatment, whereas their corresponding free peptides induced a more effector phenotype following delayed clonal expansion. Moreover, the N-terminal modification of peptides with aminooxy or alkyne linkers, which was needed for grafting onto hyaluronic acid to make hSAgA or cSAgA variants, respectively, influenced their stimulatory potency and safety, with alkyne-functionalized peptides being more potent and less anaphylactogenic than aminooxy-functionalized peptides. Both SAgA variants significantly delayed anaphylaxis compared to their respective free peptides. The anaphylaxis, which occurred in NOD mice but not in C57BL/6 mice, was dose-dependent but did not correlate with the production of IgG1 or IgE against the peptides. We provide evidence that SAgAs significantly improve the efficacy and safety of peptide-based immunotherapy.

Autoantigen Tetramer Silences Autoreactive B Cell Populations

Many autoimmune therapies focus on immune suppression to reduce symptom severity and halt disease progression; however, currently approved treatments lack specificity for the autoantigen and rely on more global immune suppression. Multivalent antigen arrays can disarm pathogenic autoimmune B cell populations that specifically recognize the antigen of interest via their B cell receptor (BCR). Disarmament may be achieved by BCR engagement, cross-linking, and sustained receptor occupancy as a result of multivalent, high avidity BCR binding. To engage and explore this mechanism, a tetramer display of the encephalogenic proteolipid peptide (PLP_139-151), referred to as 4-arm PLP_139-151, was synthesized by copper-catalyzed azide-alkyne cycloaddition chemistry. Subcutaneous administration of 4-arm PLP_139-151 completely ameliorated symptoms of paralysis in a mouse model of multiple sclerosis known as experimental autoimmune encephalomyelitis. Competitive binding of 4-arm PLP_139-151 to PLP_139-151-specific IgG in the mouse serum demonstrated the enhanced avidity associated with the multivalent array compared to the free peptide. Furthermore, key PLP_139-151-reactive B cells were depleted following 4-arm PLP_139-151 treatment, resulting in significant reduction of proinflammatory cytokines. Together, these data demonstrate the potential of 4-arm PLP_139-151 to silence autoreactive B cell populations and limit the downstream activation of effector cells.

Tetrameric Fluorescent Antigen Arrays for Single-Step Identification of Antigen-Specific B Cells

Fluorescent antigen production is a critical step in the identification of antigen-specific B cells. Here, we detailed the preparation, purification, and the use of four-arm, fluorescent PEG-antigen conjugates to selectively identify antigen-specific B cells through avid engagement with cognate B cell receptors. Using modular click chemistry and commercially available fluorophore kit chemistries, we demonstrated the versatility of preparing customized fluorescent PEG-conjugates by creating distinct arrays for proteolipid protein (PLP139-151) and insulin, which are important autoantigens in murine models of multiple sclerosis and type 1 diabetes, respectively. Assays were developed for each fluorescent conjugate in its respective disease model using flow cytometry. Antigen arrays were compared to monovalent autoantigen to quantify the benefit of multimerization onto PEG backbones. Finally, we illustrated the utility of this platform by isolating and assessing anti-insulin B cell responses after antigen stimulation ex vivo. Labeling insulin-specific B cells enabled the amplified detection of changes to co-stimulation (CD86) that were otherwise dampened in aggregate B cell analysis. Together, this report enables the production and use of fluorescent antigen arrays as a robust tool for probing B cell populations.

Antigen-specific immune decoys intercept and exhaust autoimmunity to prevent disease

Relapsing-remitting patterns of many autoimmune diseases such as multiple sclerosis (MS) are perpetuated by a recurring circuit of adaptive immune cells that amplify in secondary lymphoid organs (SLOs) and traffic to compartments where antigen is abundant to elicit damage. Some of the most effective immunotherapies impede the migration of immune cells through this circuit, however, broadly suppressing immune cell migration can introduce life-threatening risks for patients. We developed antigen-specific immune decoys (ASIDs) to mimic tissues targeted in autoimmunity and selectively intercept autoimmune cells to preserve host tissue. Using Experimental Autoimmune Encephalomyelitis (EAE) as a model, we conjugated autoantigen PLP_139-151 to a microporous collagen scaffold. By subcutaneously implanting ASIDs after induction but prior to the onset of symptoms, mice were protected from paralysis. ASID implants were rich with autoimmune cells, however, reactivity to cognate antigen was substantially diminished and apoptosis was prevalent. ASID-implanted mice consistently exhibited engorged spleens when disease normally peaked. In addition, splenocyte antigen-presenting cells were highly activated in response to PLP rechallenge, but CD3⁺ and CD19 ⁺ effector subsets were significantly decreased, suggesting exhaustion. ASID-implanted mice never developed EAE relapse symptoms even though the ASID material had long since degraded, suggesting exhausted autoimmune cells did not recover functionality. Together, data suggested ASIDs were able to sequester and exhaust immune cells in an antigen-specific fashion, thus offering a compelling approach to inhibit the migration circuit underlying autoimmunity.